The demand for fluidized shortening is rapidly increasing because of convenience in storing, pumping and metering fluid shortening compositions. In large commercial bakery operations, plastic shortening is difficult to handle. It is nearly impossible to add plastic fats continuously to batters at controlled rates.
There is presently available on the market a number of major fluid shortenings. In these cases and depending upon the composition, fluidization is normally done in a batch tempering process which takes from 18 to 36 hours to obtain a stable fluid shortening.
It is a principal object of the present invention to provide a continuous fluidization process. Advantages are inherent in any type of continuous operation. Cost can usually be reduced, the control of the operation simplified and the quality of the final product enhanced.
Fluid shortenings containing suspended solids combine the highly functional characteristics of plastic shortenings with the ease of handling of liquid shortenings. Fluid shortenings are characterized by the presence of low levels of highly functional solids suspended in a normally liquid oil matrix. The liquid oil base in most commercial products is derived from soybean oil and is entirely liquid at 60.degree. F. The type and amount of functional solids used including emulsifiers, viscosity stabilizers, conditioners, etc., depend upon the specific end use or application. Fluidized oils are used in dressing oils, cake shortenings, bread shortenings, and coffee whitener shortenings. The functional solids, particularly the stabilizers, are generally soybean base or of stable normally crystalline hard stocks having a melting point above about 100.degree. F. The functional solid type and content, and the liquid oil matrices of a fluid shortening composition have an effect on the rate of crystal transformation or fluidization. In general, the fluidized shortenings of the prior art as well as those produced in accordance with this invention, have an overall Iodine Value in the range of from about 75 to about 125.
Generally, the normally liquid triglyceride base in fluid shortenings contains very few glycerides having melting points higher than 60.degree. F., i.e., the base oil exhibits no ostensible solid phase particles at a temperature above about 60.degree. F. The normally solid glycerides or lipids remain solid at temperatures as high as about 100.degree. F. When the final suspension is cooled from 100.degree. F. to 60.degree. F., the amount of solids will not increase by more than about 20% of the solid content at 100.degree. F. That is, the solid fat index (SFI) curves for fluid shortening are relatively flat in this temperature range. Compositions containing less than 1% to 2% solids are generally unstable; that is, the solids gradually settle out. Compositions containing greater than about 20% solids are generally too viscous and approach in consistency a plastic or stiffened product.
In commercially available fluid shortenings, the percent solids at room temperature (70.degree. F.) range from about 4% to about 12% by weight. For a particular formulation having a given SFI profile and functionality, there is a specification for a centrifuge spin test which gives a measure of fluid shortening dispersion and viscosity of fluidity of the product. Stability is generally indicated at from 2% to 15% maximum free oil layer above a centrifuged sample according to the test procedure which will be described below. These two physical phenomena are generally inversely related. As the viscosity increases, separation decreases and vice versa. The storage life of fluid shortenings is specified as at least one month when shipped bulk and three to six months in a package, such as a can or a drum. During normal storage conditions or temperature cycling, the stability of a fluid shortening is manifest. During temperature lowering, solids may recrystallize in the form of interlacing crystals which impair fluidity of the shortening. The melting of solids during temperature elevation may cause separation of the liquid and solid phases. It is known that a stable fluid shortening must have a beta crystalline phase obtained from transformation of alpha or beta prime phases. (Reference may be had to the patents of Holman et al, U.S. Pat. No. 2,815,285 dated Dec. 3, 1957 and Andre et al U.S. Pat. No. 2,815,286 also dated Dec. 3, 1957). For uniformity and stability over a temperature range of from 60.degree. to 100.degree. F., at least 80%, and preferably 85% of the solids should be beta crystals. The beta stable crystals should be in a concentration such that the viscosity is low enough to enable easy pumping yet high enough to prolong suspension. (See the patents to Norris U.S. Pat. No. 3,914,452, dated Oct. 21, 1975, the patent to Reed et al, U.S. Pat. No. 3,857,985, the patents to Holman and Andre supra., and U.S. Pat. No. 3,145,110 dated Aug. 18, 1964).
The triglyceride molecules of fats, oils and shortenings exhibit four types of polymorphic forms which can be seen by X-ray diffraction spectra. (See U.S. Pat. No. 2,521,242 to Mitchell). In general, the alpha form crystallized from the liquid phase subsequentially transforms to beta prime, intermediate, and beta forms in series. (See Hoerr, C. W. "Morphology of Fats, Oils, and Shortenings", JAOCS., Volume 37., Oct. 1960). The alpha crystal has the lowest melting point and density, and is the least stable. The beta crystal has the highest melting point and density, and is the most stable. Once transformation to the more stable forms has occurred, lower polymorphs can only be obtained by completely melting the sample, crystallizing the alpha form, and repeating the transformation sequence. The readiness with which different forms crystallize from a liquid melt (alpha.fwdarw.beta prime.fwdarw.intermediate.fwdarw.beta) is in reverse order of their stability. Hence, the least stable form appears first in a super-cooled material. (A. E. Baily, Melting and Solidification of Fats, Interscience, Inc., N.Y., 1950).
Polymorphism of a lipid is basically dependent on composition of the lipid, processing, tempering and storage conditions, the effect of crystal promoters and inhibitors, (Thomas, "Shortening Formulation and Control", JAOCS, Volume 55., November 1978; Harnet, "Cake Shortenings", JAOCS, Volume 54., December 1977; MaCarthy, U.S. Pat. No. 3,796,806 dated Mar. 12, 1974). Polymorphism is most evident in commercial fats, such as, highly hydrogenated soybean oils. These fats consist predominately of a single glyceride such as, tristearin, (A. E. Baily, supra.). It is also evident in mixtures, e.g., fluid shortenings, of such fats with liquid oils of low melting point, although not normally evident in partially hydrogenated oils or fats having a wide variety of glycerides melting over a long temperature range.
Polymorphism is also exhibited in various emulsifiers commonly included in shortening compositions. Among these are the mono- diglycerides, e.g., glyceryl monooleate, glyceryl dioleate and mixtures thereof; the alkali metal or alkaline earth metal acyl lactylates, e.g., sodium stearoyl-2-lactylate; succinylated mono- and diglycerides. Such emulsifiers are well known in the art and reference may be had to Gawrilow U.S. Pat. No. 4,137,338 and the patents referred to therein for further details of such emulsifiers (note particularly columns 4 and 5 of U.S. Pat. No. 4,137,338). These lipids may be used in the shortening compositions hereof in replacement of part or all of the normally solid triglyceride component. The mono- and diglycerides are the easiest replacement lipids for use herein while the lactylates and succinylates should be used, if at all, in only partial replacement of the normally solid triglyceride and then not exceeding about 4% by weight of the shortening composition, and preferably less than 1% or 2%. The maximum tolerable amount will be found to vary with the nature of the base oil used. The ethoxylated mono- and diglycerides may be tolerated to a higher concentration, again depending on the base oil because of their apparent solubility in the base oil.
Generally, fats and oils that have Iodine Values above about 72 tend to crystallize in the alpha form, whereas those of lower Iodine Value can and do tend to transform to the beta prime form during solidification (Hoerr, supra.). It has been shown experimentally that the crystals of partially hydrogenated soybean oil, (70 I.V.) have approximate alpha, beta prime, and intermediate melting points of 68.degree. F., 77.degree. F., and 85.degree. F., respectively. Soybean flakes, (stearine) have approximate melting points of 123.degree. F. (alpha), 131.degree. F. (beta prime), 139.degree. F. (intermediate), and 145.degree. F. (beta). The crystalline melt temperatures are dependent on the extent of the plastic state and upon the Iodine Value (I.V.). It has been found that an increased proportion of higher melting triglyceride in a fat or oil, evidently enhances the transformation to more stable forms, (Hoerr, supra.). A blend of liquid oil such as lightly or partially hydrogenated soybean oil, and normally solid triglycerides such as, soybean stearine, would have a composite crystal melting point spread of its two components.
Beta stable fluid shortenings contain large crystals (5 to 50 microns in longest dimension) that tend to prolong suspension (Thomas, supra). The smaller alpha and beta prime crystals are undesirable because they are needle-like in shape and tend to interlock and stiffen the final product. Alpha crystals are very soluble and tend to dissolve and recrystallize with temperature changes. Thus, the product will grow large crystals which tend to separate into liquid and solid phases at high temperature and solidify at low temperature. (See the Holman and Andre U.S. Pat. Nos. 2,815,285 and 2,815,286, supra.). An abundance of beta prime crystals tends to cause the product to become plastic rather than to remain fluent. Cottonseed oil and lard exemplify beta prime crystal-directing triglycerides; and their normally solid derivatives, including those from hydrogenation, have a preponderantly beta prime crystal-forming tendency. Conversely, the useful normally liquid base oils for the instant process, e.g., soy oil, are beta crystal-directing, i.e., they favor the formation of the beta crystalline form of a polymorphic lipid crystallizing therefrom. Furthermore, such lipid so crystallizing in the instant process should have a preponderantly beta crystal-forming tendency. For uniformity and stability over 60.degree.-100.degree. F., at least 80% of the solid fats in fluid shortenings should be converted to the beta form. In general, fluid shortening should not contain more than about 5% by volume of entrained air or other gases. Minimization of gas entrainment improves both the physical stability and viscosity characteristics over time. (See Norris U.S. Pat. No. 3,914,452, supra.). The lower melting polymorphs incorporate numerous relatively small air bubbles. The high melting polymorphs incorporate relatively few large air bubbles. Large air bubbles in a beta crystallized shortening can be removed by deaerating under vacuum (U.S. Pat. No. 3,857,985). If the aeration properties normally associated with beta prime small crystals, as in a plastic shortening, are required in the fluid shortening application, they can be achieved by the addition of an appropriate emulsifier. (Thomas, supra.).
When producing a stable fluid shortening from a liquid melt, the initial crystallization should take place rapidly so the alpha crystals will not grow large enough to interlock or form a viscous mass. (Holman and Andre, supra.). Mild agitation during processing reduces the growth of large crystals.
After crystals of a low melting form have been produced, crystals of the next higher melting form are obtained by heating the mixture to a temperature slightly above the melting point of the low melting solid form of the solidifying lipids present and allowing transformation or melting and resolidification to take place. (Bailey, supra., and Hoerr, supra.). Less desirable non-beta crystals can be transformed to beta stable crystals by heating the initially crystallized mixture to a temperature above the melting temperature of alpha and beta prime crystals but below the melting point of solid fats in the beta crystalline form. At this temperature, the mixture contains only beta crystals in liquid oil. Upon cooling, the crystal nuclei seed the crystallization to a beta phase. (Holman and Andre, supra.).
The glycerides with the shorter chain lengths have faster rates of polymorphic transformation. Like other transformations from metastable to stable state, fat polymorphic transformation can be relatively slow. At a temperature far below its melting point, an unstable form may exist indefinitely. The rate of transformation increases with an increase in temperature. However, at higher temperatures stable beta crystals dissolve to a large extent and cannot serve as seed crystals. Upon cooling such a mixture, the shortening may then form undesirable alpha or beta prime crystals or beta crystals which are too large or coarse in size. The time required for transformation may be reduced if the shortening is mildly agitated during fluidization and tempering. In general, higher temperatures are required for compositions containing larger amounts of solids.
Fluidized shortenings are relatively new to the market, and literature on processing is scarce. The best source of information appears to be from U.S. Patents. To the best of my knowledge, no strictly continuous process is being used or is described in the art for manufacture of fluid shortenings. All of the processes investigated on a production scale involve the use of quick chilling equipment, e.g., a Votator including "A" and "B" units in some scheme to effect the initial crystallized mass or crystal nuclei prior to or during fluidization. The current process technology can be divided into batch and mixed flow processes. It is evident that practiced fluidization processes evolved from modification of processes for production of plastic shortenings.
The current Votation-batch fluidization process for the production of fluid shortenings involves charging the ingredients to a feed tank and agitating them in a molten state at a temperature of from 120.degree. to 140.degree. F., depending upon the melting point of the batch solids. The molten oil is pumped through a Votation system consisting of "A" units and "B" units in series. The exit temperature from the "B" unit is 67.degree.-102.degree. F., depending on the shortening composition. The uniform dispersion exiting the "B" unit is charged to a 80,000 pound capacity Stehling tank where mild agitation, typically 15 rpm with an 11 foot diameter paddle, is begun when the tank is half full. Agitation is continuous for 16 to 36 hours depending on the stable fluid shortening being produced. The fluidization temperature is 80.degree.-90.degree. F. Cooling water is circulated through coils to remove heat of crystallization and transformation. The Votation rate is 15,000-20,000 pounds per hour, nominally 20,000 pounds per hour (pph) votators.
The dispersion charged to the fluidization tanks initially is solids in the alpha form suspended in the liquid oil base. During the fluidization cycle, polymorphic transformation occurs, gradually producing a stable beta form solids fluid shortening. The agitation assists heat transfer and gently breaks crystal agglomerates with low shear.
A "dynamic" batch fluidization process involving batch recycling appears to be an improvement over the foregoing "static" batch fluidization system. Here, the process involves loading the liquid shortening mixture into a 60,000 pound tank with mild agitation. After filling, a portion, approximately 20,000 (pph), is rapidly chilled in a typical Votator system including "A" and "B" units in series to a temperature of 70.degree. F. A suspension of crystals is formed which is returned continuously to the warm batch. The solids formed during rapid chilling immediately melt and incrementally lower the temperature of the mass in the tank. This continues until equilibrium is reached at which point the solid crystals returning to the batch are not completely melted but are transformed from the lower polymorphic forms to the more stable beta crystalline form. These crystals act as a seed for further crystallization until the total mass of the batch is converted into a stable dispersion or suspension. The converted mass is deaerated to prevent oxidative deterioration during processing.
Starting with initial batch temperature of 160.degree. F., the mixture drops in temperature exponentially until a temperature of 76.degree. F. is reached in about 13 hours. The substantially converted mixture is then held at this low temperature for 1-2 hours to complete the conversion to beta form prior to packaging.
A more highly temperature controlled process involves "double cooling" with a controlled heat cycle. This process is described in the Holman and Andre patents, supra. Here, the ingredients are charged and agitated in a molten state and pumped through a conventional Votation system to obtain the initial crystallized mass. After initial crystallizing, the mixture is heated to a tempering or fluidizing temperature sufficiently high to dissolve alpha or beta prime form crystals or to transform these less desirable crystals to a beta form. The fluidizing tank is filled and held at a proper temperature until a desired transformation has occurred. This takes from 0.5 to 3 hours. The mixture contains basically only beta form crystals and liquid and on subsequent cooling these beta form crystals serve as crystal nuclei for seeding the crystallization.
When a high tempering temperature has been used, or when the solid content of the product is high, it may be desirable to chill the product rapidly back down to 50.degree.-60.degree. F. This crystallizes substantially all of the solid glycerides which may have melted during the tempering or fluidizing process. That is, super cooling and solidification under working is better than static precipitation of solids in storage which may cause stiffening of the product. The type of heating and cooling exchangers used after initial votation is not identified in the literature.
A summary of the processes investigated is shown in Table 1 below. This is an arbitrary listing. All of the information can not be put on a common basis because of the myriad fluid shortening products for which the processes were designed or processing data applies. The literature suggests that there is a trade-off between the equipment processing and "tempering" in storage or package. That is, processing ensures adequate conversion such that subsequent storage can maintain complete residual conversion to a stable suspension. Processes that have lower claimed fluidization times may require more control tempering or storage conditions to complete the conversion.
It is a primary object of the present invention to provide a process that significantly reduces fluidization time with high conversion to minimize further changes in storage or packaging, or control storage requirements. Truly continuous fluidization in accordance with the present invention is included in Table 1 for comparison.
TABLE I ______________________________________ FLUID SHORTENING PROCESSING METHODS FOR FULL SCALE PRODUCTION % Beta Fluidization Fluidizing Conver- Tankage/ Process (Reference) Time sion Holdup ______________________________________ A. Batch (Norris High (16-36 hrs.) 100 High 3,914,452) B. Batch w/recycle Med. (10-15 hrs.) 85(?) High (Reid et al U.S. Pat. No. 3,857,985) C. Batch w/double Low (0.5-3 hrs.) 60(?) Medium cooling and/or seeding (Holman, Andre, supra. and McCarthy U.S. Pat. No. (3,796,806) D. Continuous Fast (minutes) 90+ Low ______________________________________
The fluidized shortening compositions produced in accordance with this invention have essentially the same properties and are used in the same known manners as the fluidized shortening compositions of the prior art.